A Study of BGB-16673 Compared to Investigator's Choice in Participants With Chronic Lymphocytic Leukemia or Small Lymphocytic Lymphoma Previously Exposed to Both Bruton Tyrosine Kinase (BTK) and B-cell Leukemia/Lymphoma 2 Protein (BCL2) Inhibitors

Chronic lymphocytic leukemia is a type of blood cancer that affects people around the world. People with CLL suffer from enlarged lymph nodes, spleen, or liver, or have symptoms like night sweats, weight loss and fever. They have shorter life expectancy compared to healthy people. There is an urgent need for new treatment to prolong life and control disease-related symptoms. In this study, participants with relapsed/refractory (R/R) CLL who were previously exposed to a BTKi and a BCL2i will receive BGB-16673 or the investigator's choice of idelalisib plus rituximab (for CLL only) or bendamustine plus rituximab or venetoclax plus rituximab retreatment. The main purpose of this study is to compare the length of time that participants live without their CLL or SLL worsening between those participants who receive BGB-16673 versus the investigator's choice of treatment (idelalisib plus rituximab or bendamustine plus rituximab, or venetoclax plus rituximab). Approximately 250 participants will be included in this study around the world. Participants will be randomly allocated to receive either BGB-16673 or the investigator's choice of treatment.